I just bought a Lumia 520 for $50, no contract on Amazon. I don't have any immediate plans to use it as a phone, as we're locked in with verizon (grandfathered unlimited data + free wifi tether, we use it for our home internet).
I've only had it for two days and I think it's amazing for the price. Stuck a spare 32GB mSD card in, and it's an mp3 player, I can use it as a sudo GPS for directions with offline maps, has a decent outdoor camera, free wifi web browsing, view excel sheets natively, some anti-boredom light games and it's there for emergency calls. If my main phone dies, I can activate this with a prepaid plan for cheap (AT&T GoPhone) to get me by until I figure out/buy a new/used phone.
I can't think of anything else that can come close feature-wise for anywhere near the price, or price-wise for anywhere near the features. I have no idea how MS makes any money off this.